Viruses are small (about 20-300 nanometer (nm) in diameter) obligate parasites that can infect unicellular organisms such as bacteria, and all higher plants and animals. The viral core contains either single-stranded or double-stranded DNA or RNA and is surrounded by a protein coat. Enveloped viruses are additionally surrounded by a glycoprotein-studded cell-derived lipid membrane. Viruses cause diseases in animals and humans. Destruction of virus and/or virus-infected cells prevents and/or reduces the physiologic alterations produced in the host resulting from the disease processes associated with viral infection.
Bacteria are prokaryotic unicellular microorganisms. Bacteria occur in three basic structural forms; rods (bacilli), spheres (cocci), and spirals (spirilla). An additional higher order structure is denoted by the prefixes staph, diplo, and strepto, as in staphylococci bacteria, indicating that the individual spheres are bunched together in grape-like clusters, in diplococci, indicating paired cocci, and in streptobacilli, where the rods are associated into chain-like structures. Bacteria colonize cell surfaces causing infection and are capable of replication in both aerobic and anaerobic locations in the body.
Fungi are eukaryotic organisms that comprise the yeasts, which are unicellular, and the molds, which are multicellular organisms. Fungi can also cause disease and produce pathogenic sequelae.
Viruses, bacteria and fungi spread through a variety of means with particular routes of dissemination more common to some viruses or some bacteria or fungi than to others. For example, viruses, bacteria and fungi spread through physical contact or exposure to an infected source, such as contact or exposure to a living organism infected with a particular virus, bacterium or fungus. Spread of viruses, bacteria and fungi can also occur through an intermediary such as air, water or surfaces. Viruses, bacteria and fungi pass from one host to another and the pathogenic sequelae associated with a particular virus or a particular bacterium or fungus is a function of the microorganism and a function of the ability of the particular host to be infected or to support replication of that microorganism.
Microorganisms can be killed or rendered static by a number of physical and chemical methods. Physical methods include heat and radiation. For example, oxidation of bacterial proteins and desiccation of the cytoplasm occurs using dry heat for 2 hours at 160.degree. C. Treatment with moist heat at 100.degree. C. for 2 hours causes denaturing of proteins. Radiation (ultraviolet or ionizing radiation) can denature DNA of bacteria and fungi and the nucleic acids (either DNA or RNA) of viruses, thereby limiting their replication in a suitable host.
There are a number of chemicals that have been used to limit viral, fungal and bacterial growth. Alcohols (usually as 70% aqueous ethyl or isopropyl alcohol) act as protein denaturants in bacteria and destroy the lipid bilayer of enveloped viruses. Phenol (carbolic acid) and phenol derivatives such as hexachlorophene denature proteins in bacteria and in viral capsids. Formaldehyde (also glutaraldehyde) reacts with the amino substituents of nucleotide bases and crosslinks DNA and RNA in viruses and DNA in bacteria and fungi. Ethylene oxide gas alkylates amino groups in viruses and bacteria and is used for disinfecting dry surfaces. Ether destroys the lipid envelope of enveloped viruses. Non-enveloped viruses are not susceptible to inactivation by ether. Detergents also are good inactivators of enveloped viruses and kill bacteria by disrupting the cell membrane. Chlorhexidine gluconate disrupts the membranes of bacteria, fungi and viruses and thus displays broad antimicrobial activity.
Heavy metals such as silver, copper, and mercury are virucides and bactericides by virtue of their ability to combine with sulfhydryl groups in proteins. Mercurochrome is an organic compound of mercury that is safer than elemental mercury for use on skin, but mercurochrome is rapidly inactivated by contaminating residual organic compounds on skin that has not been sufficiently cleaned. Oxidizing agents such as hydrogen peroxide, iodine, hypochlorite, and chlorine oxidize sulfhydryl groups and are also capable of limiting microorganism growth.
A number of antiviral agents are known. These include amantadine (which blocks uncoating of virus particles in Influenza virus, type A) as well as a variety of nucleoside analogs that interfere with nucleic acid synthesis. Examples of nucleoside analogs include AZT, acyclovir, ganciclovir, and vidarabine. These drugs require virus replication for inactivation. Nucleoside analogs can cause adverse side effects because they also interfere with nucleic acid synthesis in cells of the host. Many are not effective over extended times because as viruses replicate they mutate in ways that render the drugs ineffective.
Antibiotics have traditionally been defined as chemicals made by microorganisms that kill bacteria. Except for the antibiotic rifampin, which has a mode of action in viruses that is different from its mechanism of killing bacteria, antibiotics generally have no effect on viruses. Bacitracin, the ceplialosporins, cycloserine, the penicillins, and vancomycin are all antibiotics that lead to the destruction or cessation of growing bacterial cells by inhibition of cell wall synthesis. The cephalosporins and penicillins are .beta.-lactams, cycloserine is an isoxazolidineone, and vancomycin is a glycopeptide. Antibiotics that interfere with cell membrane function include the polyenes (such as amphotericin B) and the polymyxins.
Chloramphenicol, the erythromycins, the tetracyclines and the aminoglycosides (such as streptomycin, neomycin, and gentamycin) bind to bacterial ribosomes and inhibit protein synthesis. Chloramphenicol is mainly bacteriostatic, so bacterial growth resumes after the drug is withdrawn. The erthyromycins are macrolide ring structures containing pendant amino sugar moieties. The tetracyclines are composed of four linearly-fused rings. Sulfonamides act by entering into the synthetic pathway for folic acid (and eventually the nucleic acids) in place of p-aminobenzoic acid (PABA). The chemical structure of the sulfonamides is similar to PABA. Another drug that inhibits nucleic acid synthesis is rifampin, which inhibits RNA polymerase in bacteria, thus preventing synthesis of mRNA. Resistance to antibiotics is common and can result either from mutations in the chromosomal DNA at a locus that controls susceptibility to a certain drug, or it may arise from extrachromosomal (e.g., plasmid) DNA that encodes enzymes that destroy the drug.
The potential for the presence of pathogenic bacteria, viruses and fungi in biological fluids such as saliva, tears, blood, and lymph is of major concern to health care workers and patients. Surfaces contaminated with bacteria, viruses and fungi can facilitate spread of infections. For this reason, methods for minimizing the transmission of pathogens in the home, in hospitals, and in daycare centers is important. Additionally, the usefulness of valuable food and industrial products can be destroyed by the presence of bacteria and viruses. Many antimicrobial agents are too toxic, too costly or otherwise impractical as routine disinfecting compounds. Some antimicrobial agents are unstable and become inactive over time or the microorganism develops resistance to the antimicrobial agent. As a result, there is a need for a simple, alternative, effective method for inactivating viruses and limiting bacterial and fungal growth.
International Patent Application No. WO 95/16348 discloses a method for inactivating viruses in body fluids that involves passing the body fluid through a column containing an "inactivating agent" such as charcoal or various dyes.
Photoinactivation of viruses has been described in some systems. U.S. Pat. No. 5,418,130 discloses photoinactivation of viruses in blood employing derivatives of porphyrin and psoralen. U.S. Pat. No. 4,775,625 discloses a continuous flow device for the inactivation of viruses using a combination of merocyanine dye and light. Most reports discussing virus inactivation using a combination of dyes and light limit the use of the dyes and light to the inactivation of enveloped viruses with one exception. Human rhinovirus type 5 (RV-5), a non-enveloped picornavirus, was inactivated by irradiation in the presence of a phthalocyanine dye (J. Pholochem. Photobiol. B. (Switzerland), 31; (3); 159-62, December 1995).
Photosensitization of bacteria has also been described in some systems. For example, Malik et. al. (Photodynamic Therapy: basic principles and clinical applications, edited by Narbara W. Henderson and Thomas J. Dougherty, published by Marcel Dekker, Inc., p. 98, 1992) described susceptibility of gram-positive bacteria, but the resistance of gram-negative bacteria, to photosensitization by hematoporphyrin. Minnock et. al (J. Photochem. and Photobiol. 32:159-164, 1996) described the use of a water soluble zinc phthalocyanine dye and light to kill gram-positive and gram-negative bacteria. Okamoto et. al (Las. Surg. Med., 12: 450-458, 1992) described the bactericidal effect of light in combination with thiazines, oxazines, xanthenes, acridines, phenazines or phenylmethane dyes on S. sobrinus. Azo dyes were ineffective at killing S. sobrinus in their study.
Some azo dyes have been used to inactivate viruses and bacteria. International Patent Application No. WO 92/22610 discloses bisazo dyes for non-photoinduced inactivation of viruses. Additionally, Pal et al. (AIDS Res. Hu. Retroviruses, 7(6): 537-543, 1991) have demonstrated the inhibition of infectivity in vitro of CD4 cells by HIV-1 in the presence of Evans Blue or Trypan Blue using non-photoinduced methods. New photo-inducible compounds are needed and, in particular, there remains a need for new antimicrobial compounds and methods that can inhibit growth of more than one type or family of microorganism.